{} .a Time Trial Frame {}

.a Time Trial Frame.

18/08/15

This is the first commission I’ve received that I’ve agreed to take on. I’ve had a few request in recent years but apart from the commitment over such a long period, I’ve also been reticent to expose another persons safety to an as yet unqualified structural integrity. As I’ve mentioned before one of the key qualities to building for me is that it remains a practical exercise of trial and error, it’s quite a different thing however to exposes someone else to this method.

So the deal here was that the commission was taken on with the commissioner (as it happens an engineer) involved. He would specify the geometry and as much as he could witness the build for himself. I’ll test ride the frame and he can make an assessment before he rides it with intent.

It was a tough build, harder than I expected, with a number of key issues to negotiate. I was interested in frame stiffness and aerodynamics. Weight was always going to be difficult to keep down – it is a large frame with over-sized tubing and I would inevitably want to over engineer the tubes and joints. So I would concentrate on fit, aerodynamics and finish and let the weight take it’s own path. In the end I aimed for a comparative weight to the Argon 18 E-116. By no means a super light frame but at least then my effort would be comparably to a legitimate machine. With the ISP and fork installed this was achieved.

The finished frame commission.

The nervous moments after a year of development and just before a test ride.

I wanted the finish to be exposed layers of carbon without the, as I call it, decorative top layer.

The bottom bracket area… as you can see i still have to attach the front hanger that I’ve just finished making and route cable through to the front mech.

We went for a 1 1/8 head tube to keep the front end profile down. I couldn’t find another TT specific alternative available to order. It’s not clear here but the head tube is profiled to a point to help push the airflow sideways.

A complete donor bike has been bought and these are amongst the other components the beautiful Reynolds wheels that will be attached. The fork we’re looking to install is a Deda TT fork.

The build story…

03/10/14

So with the help of Brian at Impact Cycle http://www.impactct.co.uk/ and Geoff at TrailNet http://www.trailnet.org.uk/ two people I more or less met out riding, this morning we had a bike fit and drew up the geometry for the TT project. Next step is to research and build a curing oven to allow us to use some Prepreg carbons, and also to do some R&D on shrink tapes that compress at high temperatures. None of this I’ve attempted before so it will be a learning curve.

This is the geometry that was generated. It’s based on a Kestrel frame that Geoff has happily ridden for years.

07/11/14

Black epoxy filler, should help with those pesky blemishes – next to the shrink tape i’ll be experimenting with.

08/11/14

This is the chosen rear end.

Glued and mounted the gear stop on the selected TT rear end. It comes in at around 350g as it is. I’ll lose more of that total with a reduction in the mono stay length. The previous rear ends I’ve used were more like 200g.

The seat stays are pretty aero and the chain stays are quite chunky so I predicted it would serve me well. It has a conventional brake mount which we were all happy with, we didn’t want to add too many complications although I suspect it would be pretty simple to mount the brake under the BB area.

I began construction on the seat tube, the tubes have bulkheads running through in an attempt to increase rigidity against torsional forces… at least that’s the theory, at the very least it will increase the stiffness of the foam to allow me to create the really narrow airfoil shape.

As before the foam is shaped on a long strip of sand paper. I created the carbon strip by pressing layers of unidirectional carbon between two sheets of (flat) glass.

23/01/15

Seat tube progress.

31/05/15

You can see the bulkhead more easily in this top tube off cut. There are two bulkheads running up the seat tube from the bottom bracket. Probably unnecessarily there’s a continuous section running through the top tube and also sections in the down tube meeting the head tube and bottom bracket. I didn’t want a continuous section in the down tube as it would play havoc with internal cable routing.

The carbon arrives. After a conversation with Hana Kolarova and engineering student and sponsored rider, who happens to be building a frame as part of her studies, she passed on some of her research. It suggested aiming more specific 0/45o biaxial cloth at the head tube and BB areas which of course makes sense but seeing the data really forces it home. It’ll be interesting to experience the outcome.

I tend to use tailors chalk and a very thin slice of masking to demarcate the cutting line and either use scissors or a guillotine blade to cut down the tape line. This method stops the fabric from fraying and the tape tends to easily peel off when resin is applied.

I worked with the slotted 68mm BB shell as usual but this time I generated a sleeve rather than using the available carbon box as I’d done before. This would commit me to routing gear cable externally over the BB area. I plan to drill out the Ali shell, mainly so that when I adhered it there will be even more resistance to an over tightened bottom bracket twisting the shell. Whilst I don’t have experience of this myself, I’m told that it’s a common problem.

Wrapping and vac bagging the tubes.

On this occasion I have chosen to work with a low viscosity resin that should flow through the fiber more easily, in addition I’ve chosen a slow catalyst that should allow the vacuum time to remove more excess resin than I’d managed with the less viscous fast drying products. In addition the new resin has a post cure capacity at a higher temperature, which basically means I can knock up an oven and bake the frame to a harder finish. I was going to use pre pregs however i could find the variety of cloth required.

03/2015

First working layer on the seat tube, top tube and BB shell. I’ll shape the integrated rear wheel shape into the seat tube next. It’s easier to shape when the tube has some rigidity.

The width of the mono stay fitted really well onto the seat tubes, a super strong fixing will be easy.

You can see more clearly here the variation of fibers applied. Depicted here is the 0/45o fiber.

Next was to set the frame into the jig. I really need to make a proper jig, I’m more or less happy that the material I work with can be aligned however I do spend a great deal of time checking and double checking, there are more full proof home made solutions.

08/04/15

After applying a few layers to the original cores I’m assessing the frame in the jig before completing the individual tubes. The next layer will be several layers of uni directional cloth around the ISP and several layers of +/- 45o biaxial cloth around the head tube and BB join areas. The rear end mounts nicely onto the seat tube. It was tricky to assess the length of the seat tube against the arc of the rear wheel aperture.

06/04/15

Finally the TT frame tubes have been bonded. It’s fairly neat and considering the amount of carbon used a starting weight of 1.1kg gives me a fair amount to play with when shaping the tube intersections.

05/06/15

I was interested to see how this Fairing Compound will work on the TT joint filet’s. They use it on plane wing construction, and as it says it’s super light. The contents of this entire 1ltr tub weighs just a few grams! l believe Guru Cycles use something similar, a molding putty on their joints before the layups so I thought this might also work. You mix just a little resin into the compound and it sets hard to a sand-able finish.

09//06/15

I cut paper templates that fitted the frame before cutting the full compliment of layers to be applied to the joints.

11/05/15

30/05/15

04/01/15

I’ve just begun constructing the oven to facilitate the curing process of the resin.

I stripped back an old storage heater, removed the bottom cage and thermostat. I bought a simple chef’s thermometer with an alarm and stuck the probe through into the oven. The walls of the oven are made from 50mm storage insulation that has no ignition point… meaning it can’t catch fire. Anyway the top temperature I’m aiming at is only 80o so it’s not a huge concern. I don’t really have room for the oven so I’m really only looking at a one off use.

Finished oven. Trialed it last night, the issue became ways of keeping the temperature down, it heats up super fast.

I cooked the frame for 6hrs at 40o and then a further 7hrs at 60 – 70o. The M3 structural adhesive is also a high temperature product so the entire frame post cured nicely. Following this I applied several thin layers of a UV resistant resin. I chose to apply this with a ribber glove. I spread a very small quantity over the frame and once dry buff back with a polishing compound and then reapply. The process removes the high gloss finish that I not so keen on.

It’s nice to do this on a hot day and cure the resin quickly. I chose the expose the fiber layups on this frame. I think it really looks nice and is by far the most blemish free frame I produced to date.